i just pieced together the components needed for a 300w Cob LED and it comes to around $650. thats really not too bad when you consider you wont be buying bulbs again. thats using top of the line cree LED's as well im sure u could do it cheaper if u wanted to.
out of interest for myself i pieced together a 800w to cover a 1.5m tent at around $1500 which is actually pretty bloody good considering they are asking $1500 for the double 315w dpap CMH i am currently using (although i only paid half that at the time i bought it)